This invention relates to a fault detection circuit and more particularly to a fault detection circuit suitable for detecting faults in the sensor circuitry of an anti-skid control braking system and indicating the same to a driver of a motor vehicle having such braking system.
Increasing demands have been placed on the safety of the operation of motor vehicles. In response to these demands, industries have placed great emphasis to finding ways to improve the braking system of motor vehicles. As a result, a system providing dynamic control of the braking operation has been developed for preventing noncontrolled skidding caused by excessive braking of the vehicles wheels overcoming the frictional forces between the tires of the vehicle of the road surface. These types of braking systems are known in the industry as anti-skid control systems.
Briefly, the anti-skid control system includes a sensor coil fixedly mounted to each wheel, and a magnetic breaker element which rotates at the rotational velocity of the wheels. The sensor coil and the magnetic breaker element cooperate to provide an output signal of which the magnitude and frequency is related to the rotational velocity of each wheel. The output signal from the sensor coil is applied to other circuitry which electronically controls the braking force applied to the wheels when slowing the vehicle. Thus, the anti-skid control system prevents uncontrolled skids from occurring because of too much braking force being applied to the wheels.
It is contemplated that after a period of time to adjust to the operation of such anti-skid control systems, that drivers of vehicles having these systems will rely on them to control the braking of the vehicles. Since the anti-skid control system is employed to override too much pressure being mechanically applied by the driver to the brakes, safer operation of vehicles is envisioned. However, if for some reason the anti-skid control system becomes inoperable due, for example, the sensor coil being open circuited or shorted either to a ground reference potential or to a power supply potential, disasterous results could result. The driver, being psychologically conditioned to expect the anti-skid control system to control the braking operation, could unknowingly apply too much force to the brake which could cause the vehicle to skid. Moreover, as the anti-skid control system provides for quicker stopping, a driver relying on an undetected system failure might not allow enough braking distance to prevent a collision of some sort. Therefore, a need exists to provide a fault detection circuit to warn the driver when the anti-skid control system is inoperable so that the driver can rely on the mechanical braking system and adjust accordingly.